This document relates to information hiding.
Secure communication can be defined as a means of information sharing between two parties, where no third party is aware of the communication or the information exchanged. Information about a secure communication ranges from the content of the message and the communicating parties to the fact that a communication took place. In some past approaches, the security of content information was ensured by using encryption. However, since ciphering can arouse suspicion, information hiding techniques that embed messages in cover-text to produce stego-text are now widely used. Because of the emergence of digital copyright protection techniques, information hiding schemes have also received a great deal of attention in the last decade. In particular, watermarking, which tries to protect copyright ownership, and fingerprinting, which is used to identify copyright violators, have been well studied. Criteria used to assess information hiding techniques include robustness, security, and capacity. Robustness is the resistance of the embedded message to modification or erasure in the stego-text. For instance, the criterion requires an information hiding system to be robust against common signal processing and geometrical distortion algorithms. The objective of this security constraint is to prevent a malicious user who knows the system from discovering loopholes in it. The long-held wisdom in the field of security is summarized by Kerckhoff's principle, which advocates that security cannot rely on the assumption that an opponent is unfamiliar with the system. Rather, it must be assumed that the opponent knows the system except for a few keys or parameters. The capacity criterion refers to the amount of information that can be embedded in the cover-text.
Referring to FIG. 5, a conventional paradigm of information hiding can be described as follows. Let us assume that Alice wants to send a secret message m to Bob. Alice uses a secret encoding key to embed the message in the cover-text X and obtain the stego-text {tilde over (X)}, which is then published. A decoding key, which Bob will use to open {tilde over (X)} and retrieve the message m, is then derived. The key can be published or transmitted secretly to Bob. If it is publicly available, then the scheme is defined as asymmetric watermarking, which means that the encoding key is private and the decoding key is a publicly available. Otherwise, the scheme is defined as watermarking, which indicates that both the encoding and decoding keys are secret. Note that in asymmetric watermarking, the decoding keys are usually content-dependent and managed by a trustworthy third party in order to maintain their integrity. Because the secret message is implanted in the cover-text, the latter is modified, which is a side-effect of using the conventional paradigm for hiding information.